Magnet system with movable coil



J. WOUDA March 11, 1958 MGNET SYSTEM WITH MOVABLE COIL Filed June 17, 1952 l lIlIllI-ll-lIl-.ll'llll'---EBI Invenor Jun WOUDA Attorney United States Patent fC F MAGNET SYSTEM WITH MOVABLE CGIL Jan WoudmVechtem-near Utrechty Netherlandsiiasaignor to N. V.` Nederlandsche..Instrumenten en.-.Electrische Apparatenfllabriek .Nieaf, Utrecht, Netherlands, a companyof` the Netherlands Application-June 17, 1952,S'eriallNo. 293,912?

Claims priority, application NetherlandsJuneL 19.51 Claims. (Cl. 321-1151) The inventionV is concerned. with ajmagnet system for electrical measuring instruments, relays, land the like, with a movable coil and aV permanent; magnet of ferromagnetic materialr with high coercive. force and particularly ofthe type in which the coil, through the interaction of the iield produced by the current inthe lcoil and the lield of the permanent magnet, is dellected about a cylindricall core of permanentmagnetic material whose magnetic flux is closed back byv a structure of rsoft iron. which leaves a narrow air gap between the core and said structurethrough which gap the coil moves.

Morek particularly, the invention is concerned with a novel arrangement of the ferromagnetic partsb of the magnet systemrelatively to the coil such that the' 4mag-v netic circuit is built'up. with a leakage as small as possible and for highest eiiiciency and fullest' utilizationjof the magnetic energy ofthe system. This is achieved when, in accordance with the invention, the core-of the" permanent-magnetic material is in form of a at., generallyy circular disc, that is a disc of. a diameter exceeds ingthe height dimension ofthe disc. The disc is .permanently magnetized diametrally. The magnetic return path for'closirig backthe magnetic ilux ofthe core is constituted by a plate or a pair of `plates of `maglletizabl'e soft iron disposed opposite and extended over one, .or each plate over one,l of the end faces of the .d isc, parallel' thereto and vspaced apart therefrom soY as to l'eayea narrow air gapl or narrow air gaps therebetween, for the passage of the magnetic flux, produced by the core, in' the axial direction of the disc. A rotatable coil with. means for suspending it is disposed at the magnet system with the axis of suspension and rotation coaxialA with the disc. The coil is extended With one of its legs or both legs through the air gap or air gaps, the 'legs thus crossing the axis and the flux.

Through this structure theY coil is and remains `removable from the magneticsystem and may bev replaced without the' necessity of'detaching any part of the magnetic system. This system, therefore, once magneti'zed to produce its permanent magnetism need not be magf netized again when the coil had been removed and re.- placed.

Since during this operation the magnetic circuit remains unaifected, no lossv of magnetization nor any diminishing of the flux from its original intensity, thus no change of the `adjustment of the instrument will be experienced.

The air gap or gaps within whichthe leg or legs of the coil are subjected to the deflecting forces through the interaction .of the fields thus cross the axisA of suspension. ofthe coil in vcontrast with conventional :structure whereA the magnetic air gap within which the legs of the coil are subjected to the dellecting forces and thus move surrounds peripherally the core magnet.

-For further explanation lof the invention and-forv its illustration, various of its embodiments will now be set forth in the ensuing speciiication and will be illustrated in and by the accompanying drawings which are to be 2,826,739 Patented Mar. 11, 1958 ICC 2. understoody illustratiite. of theqinventionand. not limitative of vits scope. Other Yembodiments incorporating the principle` -underlyilgz` my .ilventi'QD `are feasible vwithout departing from thev .snit-it.and` ambit of.' my appended claims..

In the drawings;A

Figs, 1 andy 2'. respectively are a. rather diagrammatic. plane view and an elevational' view of! an embodiment off the .magnet systemof the ,invention illustrating the. principle. thereof;

. Eig. 3l is a plan view illustrating the mode in which the system. is. diametrally magnetized; f

Figs. 4 and 5 andf 7f,. 8 and 9A, and l0 and ll,are respectively plan views.. .and .elevational viewsv of various embodiments ofthe invention.

Figs. 1` and. 2 illustrate-.the principle ofthe invention. 11l designates the core, inthe. example illustrated', in the form of a at, circular disc ofpermanent-magnetic material; The magnetic flux is closed back by ferromagf netic pieces. 12, 13,f, inthe form of" plates of soft iron disposed injuxtaposition. to the core or disc` 11 at both faces thereof and I'eayingav narrow gap 14,v 1'5' respectively, at each of the. faces ofthe core 4between core .and plate.

The moving coil, designatedv by 16 is. suspended by meansof`its axle arms 1'7,y 18, between appropriate bear ings 19, 20 .as conventional rin the art. '.Slots. 24v are. provided'` in the plfatesl,V 1.3,', and extended radially outwards so that the axles 1'1",-` 18may he Passedl through and along these. slots when the coil' .is to. be removed fromtthe. magnet system Oris ,to he replaced.

Although two yferromagnetic plates1j2`, ,13 are kshown in Figs. 1 and 2.one .of these plates may be omitted without departing from ,the principley of the invention.

Fig. 3 illustrates how the-corel magnet of Figs. l and' 2 may be magnetzed. Two' pole shoes .2.5, 26 otsoft iron are applied to the sideslof the core.` magnet 1l, l

whereupon, .for instance by means of a. Streng electromagnet',y not shown in Fig, 3, a liux ofsuchstrengthis sent throughthe core 11 that it will be saturated. After removal of the pole shoes 25, 26, the magnetic lines of force Will haveV approximately the course ,as shown in Fig, 2 by dash lines with arrows.

In Figs. 4 andV 5 afstructural embodiment of. a magnet system of the invention is illustrated. vIt should be noticed, however, that' in order to show more clearly the essential' features of the invention there. have Ibeen. omitted from the showing of Figs. 4 toll all details not essential for the illustration of theA iiiyentiorn4 details as such which may serve Yfor the' mounting o r vsecuring of the various parts, bearings,y screws, spiralsprings, or. the like.

In these embodiment the plates 12, 1? of. soft iron are joined together by means o f studs or spacers Y29,30.

Betweenthe soft iron plates 12, 1,3,and the core magnet 11, there may `be provided spacing discs.` 31. of nonf.

magnetic material,l brass for instance, of s uchshape that movement. of the moving coil is not impeded while nevertheless they present contact faces aslarge as. posa. sible. By means. of these spacing discs. 31 thecore. magnet 11 will.' be. secured in spaced relationship. bef. tween the rsoft ironplates 121-3, by clamping, solderingor brazing, cementing, or otherwise. YWhen a. proper opening. or bore is4 providedin the. core magnet, `a rivet or `screw may also be employed for .joining the'. parts: together.

In Figs. 6 and 7, in order to control the configuration@ ofl the magnetic: field, thecore magnet 1'1' ,isprovided at its faces with pole shoes 34, 35, and k36, 37, respectively, of soft iron projecting into the air gaps 14, 15.

Through this means the torque which is operative on 3 the coil in any of its positions may be predetermined at will so that the character of calibration of the scale of the instrument may be adapted to prevailing requirements. In this way, a calibration of the scale of proportional character may be obtained.

Another possibility of attaining this result is illustrated in Figs. 8 and 9. In this embodiment the circumference of the core magnet 38 is not of circular contour but deviates therefrom. The deviation may be an elongation of the contour in one direction such as for instance transversely of the direction of magnetization. In this way too the character of the scale graduation may be modified. The form of the core disc 38 as illustrated results in a nearly proportional graduation of the scale. By selection of any other shape, the graduation of the scale may, within certain limits, be chosen at will.

It is also possible to control the configuration of the ilux by shaping the soft iron plates appropriately. An embodiment illustrating this feature is shown in Figs. 10 and 1l where pole shoes 41, 42, and 43, 44, respectively projecting into the air gaps are provided at the soft iron plates 12, 13, on the surfaces thereof which face the air gaps. The shape of these pole shoes may be chosen as desired. The same purpose may be achieved by providing for an appropriate form of the soft iron plates themselves instead of providing them with pole shoes, or additionally thereto.

ln all embodiments shown it is also possible to`control the configuration of the lines of force by selecting an appropriate direction or axis of magnetization, for instance by applying in the magnetizing arrangement of Fig. 3 the pole shoes 25, Z6, to the core magnet 11 in another direction or position than that illustrated.

It is also possible to employ a core not totally of permanent-magnetic material but to employ such ma terial for instance only for the central part of the core and make the remaining part or parts of soft iron.

The invention is also applicable in instruments where several permanent-magnetic cores and several coils, more than one of each, are employed.

In any case the coil may be readily removed and replaced without any interference of the structure of the magnet system.

WhatIclaim is:

1. A magnet system for use in electrical measuring instruments, relays and the like, 'comprising acore of permanently magnetized material shaped in theform of a substantially circular disc having two parallel faces, said core being magnetized across its diameter, said disc having a diameter exceeding the height dimension thereof, a magnetic ux carrying member xcomprising at least one plate of ferro-magnetic material disposed opposite one of said core faces in spaced, parallel relationship thereto and forming a narrow air gap for the passageof magnetic flux produced by said core in a direction generally parallel to the central axis perpendicular to the face of said core, said plate being at least as wide as the face of said core adjacent thereto, a rotatable coil disposed around said core, means for rotatably mounting said coil with its axis of rotation coaxial wit-h said axis of the core, said coil being arranged insaid air gap and around said core, said coil `being adapted to be connected to an electrical circuit and to be rotated yby the interaction of the current in said coil with said liux uniformly over a wide arc about the circumferential face of said core, and said plate being provided with a slot extending radially outwardly from its center to permit the removal and replacement of said coil without disturbing the structural and magnetic relationship of the core and said plate.

2. A magnet system as described in claim 1, and iu- 4- cluding pole shoes mounted on said plate and with said shoes protruding into said air gap.

3. A magnet system as described in claim l, further comprising two plates and having pole shoes mounted on each of said plates and said pole shoes protruding into said air gap.

4. A magnet system for use in electrical measuring instruments, relays and the like, comprising a core of permanently magnetized material in the form of a substantially circular disc of a diameter exceeding the height dimension thereof, said core having two substantially llat faces parallel to each other, said core being permanently magnetized across the diameter, a magnetic return path for carrying the flux of said core which comprises two plates of ferro-magnetic material each. disposed opposite one olf said core faces in spaced parallel relationship thereto and forming a narrow air gap with said core for the passage of the magnetic ux produced by said core in a direction substantially parallel to the central axis perpendicular to the face of said core, each of said plates being at least as wide as the circular core face opposed thereto, a rotatable coil arranged around said core, means for rotatably mounting said coil with its axis of rotation coaxial with said axis of said core, said coil having a side extending through each of said air gaps, said coil being adapted to be connected to an electric circuit and to be rotated by the interaction 0f the current in said coil with said ux uniformly over a wide arc about the circumference of said circular core, and non-magnetic spacing means disposed between said core and said plates for maintaining the same in a xed spaced relationship.

5. A magnet system for use in electrical measuring instruments, relays and the like, comprising a core of permanently magnetized material in the form of a substantially circular disc of a diameter exceeding the height dimension thereof, said core having two substantially flat faces parallel to each other, said core being permanently magnetized across the diameter, a magnetic return path for carrying the flux of said core, said magnetic return path comprising two plates of ferro-magnetic `material each disposed opposite one of said core faces in spaced parallel relationship thereto and forming a narrow air gap with said core for the passage of magnetic tlux produced by said core in a direction substantially parallel to the central axis peipendicular to the `'face of said core, each of said plates being at least as wide as the circular core face opposed thereto, a rotatable coil disposed around said core, means'for rotatably mounting said coil with its axis of rotation coaxial with said axis of said core, said coil having a side extending through each of said air gaps, said coil being adapted to be connected to an electric circuit and to be rotated by the interaction of the current in said coil with said flux uniformly over a wide arc about the circumference of said circular core, and each of said plates being provided with a slot extended, radially outwardly from its center whereby removal and replacement of saidcoil without disturbing the structural and magnetic relationships of said core and said plates is facilitated.

References Cited in the le of this patent UNITED STATES PATENTS 819,071 La Roche etal May l, 1906 1,920,764 Nickle Aug. 1, 1933 1,927,346 Lawrence Sept. 19, 1933 2,509,893 Taylor May 30, 1950 2,573,183 Chudyk Oct. 30, 1951 2,607,812 Lederer Aug. 19, 1952 FOREIGN PATENTS 514,349 Great Britain Jan. 2l, 1938 

